1. Field of the Invention
The present invention relates to a blood analysis system and to a method for regulating a blood analysis system.
2. Description of the Prior Art
A large amount of important information about a patient can be obtained from blood. A blood analysis can supply information about blood gases (e.g. P0.sub.2 and pCO.sub.2), pH value, metabolites (e.g. glucose and lactate), ions (K.sup.+, Na.sup.+, Ca.sup.++ and Cl.sup.-), hormones, antibodies, DNA, etc. One known blood analysis system is described in the article "Integrated P0.sub.2, pCO.sub.2, pH sensor system for online blood monitoring", Gumbrecht et al., Sensors and Actuators B, 18-19 (1994), pp 704-708. The known blood analysis system includes a tubing system which is connected to a patient's blood system and to two containers for different calibration fluids and to a collection vessel for spent fluids and blood. Pumps are arranged at the containers to pump fluids through the tubing system, and a measurement device is arranged in the tubing system to analyze blood samples. When a blood sample is to be analyzed, the pump at the collection vessel pumps blood from the patient toward the collection vessel until the measurement unit has filled with blood. The blood's oxygen, carbon dioxide and pH value are then determined by dedicated measurement sensors in the measurement unit. The calibration fluids are employed for two-point calibration of the measurement sensors in the measurement unit while simultaneously flushing all residual blood, which could otherwise affect subsequent measurements, out of the measurement unit.
The known system consumes a small amount of blood, i.e. about 15 .mu.l, in each measurement. In other known systems, blood is pumped back to the patient's blood circulatory system.
Regardless of whether blood is consumed or pumped back to the patient, all the known blood analysis systems of this type have certain shortcomings. The blood analysis system must operate for years. The properties of pumps and tubing can change during usage or fail in some way. For example, pumps, usually peristaltic pumps, could affect the geometry of tubing so that the pump's capacity changes. Tubes could start leaking or become occluded, thereby affecting the flow of fluids in the tubes. As a rule, larger than necessary volumes are pumped to ensure that the correct amount of fluid (blood or calibration fluid) really is present in the measurement unit, thereby increasing the consumption of fluids. The only monitoring normally available is to recognize the unreasonable results which arise in the analyses of blood samples when major faults occur. Correcting a fault at this stage makes greater demands on both staff and equipment than if an alarm had been triggered before the fault became excessive. A number of erroneous measurements might have been made before the fault became big enough to affect measurements to any significant extent.